Complexation of Nickel(II) with Guanosine 5'-Monophosphate and Inosine 5'-Monophosphate: A Potentiometric and Calorimetric Study

The constants (K(s)) and enthalpies (DeltaH(s)) for stacking interactions between purine nucleoside monophosphates were determined by calorimetry; the values thus obtained were guanosine as follows: K(s) = 2.1 +/- 0.3 M(-)(1) and DeltaH(s) = -41.8 +/- 0.8 kJ/mol for adenosine 5'-monophosphate (5'AMP); K(s) = 1.5 +/- 0.3 M(-1) and DeltaH(s) = -42.0 +/- 1.5 kJ/mol for guanosine 5'-monophosphate (5'GMP); and K(s) = 1.0 +/- 0.2 M(-1) and DeltaH(s) = -42.3 +/- 1.1 kJ/mol for inosine 5'-monophosphate (5'IMP). The interaction of nickel(II) with purine nucleoside monophosphates was studied using potentiometric and calorimetric methods, with 0.1 M tetramethylammonium bromide as the background electrolyte, at 25 degrees C. The presence in solution of the complexes [Ni(5'GMP)(2)](2)(-) and [Ni(5'IMP)(2)](2)(-) was observed. The thermodynamic parameters obtained were log K(ML) = 3.04 +/- 0.02, log K(ML2) = 2.33 +/- 0.02, DeltaH(ML) = -18.4 +/- 0.9 kJ/mol and DeltaH(ML2) = -9.0 +/- 1.9 kJ/mol for 5'GMP; and log K(ML) = 2.91 +/- 0.01, log K(ML2) = 1.92 +/- 0.01, DeltaH(ML) = -16.2 +/- 0.9 kJ/mol and DeltaH(ML2) = -0.1 +/- 2.3 kJ/mol for 5'IMP. The relationships between complex enthalpies and the degree of macrochelation, as well as the stacking interaction between purine bases in the complexes are discussed in relation to previously reported calorimetric data.     

Opportunities in the industrial biobased products industry

Approximately 89 million metric to forganic chemicals and lubricants, the majority of which are fossil based, are produced annually in the United States. The development of new industrial bioproducts, for production in stand-alone facilities or biorefineries, has the potential to reduce our dependence on imported oil and improve energy security. Advances in biotechnology are enabling the optimization of feedstock composition and agronomic characteristics and the development of new and improved fermentation organisms for conversion of biomass to new end products or intermediates. This article reviews recent biotechnology efforts to develop new industrial bioproducts and improve renewable feedstocks and key market opportunities.     

Electron-nuclear double resonance spectroscopic evidence that S-adenosylmethionine binds in contact with the catalytically active [4Fe-4S](+) cluster of pyruvate formate-lyase activating enzyme

Pyruvate formate-lyase activating enzyme (PFL-AE) is a representative member of an emerging family of enzymes that utilize iron-sulfur clusters and S-adenosylmethionine (AdoMet) to initiate radical catalysis. Although these enzymes have diverse functions, evidence is emerging that they operate by a common mechanism in which a [4Fe-4S](+) interacts with AdoMet to generate a 5'-deoxyadenosyl radical intermediate. To date, however, it has been unclear whether the iron-sulfur cluster is a simple electron-transfer center or whether it participates directly in the radical generation chemistry. Here we utilize electron paramagnetic resonance (EPR) and pulsed 35 GHz electron-nuclear double resonance (ENDOR) spectroscopy to address this question. EPR spectroscopy reveals a dramatic effect of AdoMet on the EPR spectrum of the [4Fe-4S](+) of PFL-AE, changing it from rhombic (g = 2.02, 1.94, 1.88) to nearly axial (g = 2.01, 1.88, 1.87). (2)H and (13)C ENDOR spectroscopy was performed on [4Fe-4S](+)-PFL-AE (S = (1)/(2)) in the presence of AdoMet labeled at the methyl position with either (2)H or (13)C (denoted [1+/AdoMet]). The observation of a substantial (2)H coupling of approximately 1 MHz ( approximately 6-7 MHz for (1)H), as well as hyperfine-split signals from the (13)C, manifestly require that AdoMet lie close to the cluster. (2)H and (13)C ENDOR data were also obtained for the interaction of AdoMet with the diamagnetic [4Fe-4S](2+) state of PFL-AE, which is visualized through cryoreduction of the frozen [4Fe-4S](2+)/AdoMet complex to form the reduced state (denoted [2+/AdoMet](red)) trapped in the structure of the oxidized state. (2)H and (13)C ENDOR spectra for [2+/AdoMet](red) are essentially identical to those obtained for the [1+/AdoMet] samples, showing that the cofactor binds in the same geometry to both the 1+ and 2+ states of PFL-AE. Analysis of 2D field-frequency (13)C ENDOR data reveals an isotropic hyperfine contribution, which requires that AdoMet lie in contact with the cluster, weakly interacting with it through an incipient bond/antibond. From the anisotropic hyperfine contributions for the (2)H and (13)C ENDOR, we have estimated the distance from the closest methyl proton of AdoMet to the closest iron of the cluster to be approximately 3.0-3.8 A, while the distance from the methyl carbon to the nearest iron is approximately 4-5 A. We have used this information to construct a model for the interaction of AdoMet with the [4Fe-4S](2+/+) cluster of PFL-AE and have proposed a mechanism for radical generation that is consistent with these results.     

A direct functionalization of tertiary alkyl bromides with O-, N-, and C-nucleophiles

Silver oxide used in stoichiometric amounts promoted the direct functionalization of tert-alkyl bromides and provided the desired adducts in 39-96% isolated yield. Reaction of tert-bromides with carboxylic acids yielded esters, with alcohols and phenols yielded alkyl and aryl ethers, with amines and anilines yielded selectively mono-alkylated amines and anilines, and with a C-nucleophile yielded an all-carbon quaternary hydrocarbon. The method was applied to a sequential alkylation of a primary amine with two different alkyl bromides yielding selectively a tertiary amine with three different substituents in one-pot.     

Synthesis and characterization of heterodinuclear Ln(3+)-Fe3+ and Ln(3+)-Co3+ complexes,bridged by cyanide ligand (Ln3+ = lanthanide ions). Nature of the magnetic interaction in the Ln(3+)-Fe3+ complexes

The reaction of Ln(NO3)3.aq with K3[Fe(CN)6] or K3[Co(CN)6] in N,N'-dimethylformamide (DMF) led to 25 heterodinuclear [Ln(DMF)4(H2O)3(mu-CN)Fe(CN)5].nH2O and [Ln(DMF)4(H2O)3(mu-CN)Co(CN)5].nH2O complexes (with Ln = all the lanthanide(III) ions, except promethium and lutetium). Five complexes (Pr(3+)-Fe3+), (Tm(3+)-Fe3+), (Ce(3+)-Co3+), (Sm(3+)-Co3+), and (Yb(3+)-Co3+) have been structurally characterized; they crystallize in the equivalent monoclinic space groups P21/c or P21/n. Structural studies of these two families show that they are isomorphous. This relationship in conjunction with the diamagnetism of the Co3+ allows an approximation to the nature of coupling between the iron(III) and the lanthanide(III) ions in the [Ln(DMF)4(H2O)3(mu-CN)Fe(CN)5].nH2O complexes. The Ln(3+)-Fe3+ interaction is antiferromagnetic for Ln = Ce, Nd, Gd, and Dy and ferromagnetic for Ln = Tb, Ho, and Tm. For Ln = Pr, Eu, Er, Sm, and Yb, there is no sign of any significant interaction. The isotropic nature of Gd3+ helps to evaluate the value of the exchange interaction.     

Geometric Properties of Symmetric Spaces with Applications to Orlicz–Lorentz Spaces

We deal with the basic convexity properties –rotundity, and uniform, local uniform and full rotundity –- for symmetric spaces. A characterization of Orlicz–Lorentz spaces with the Kadec–Klee property for pointwise convergence is given. These results are applied to obtain criteria of convexity properties for Orlicz–Lorentz sequence spaces, and some new proofs of the sufficiency part of criteria for rotundity and uniform rotundity for Orlicz–Lorentz function spaces.     

Photochemical synthesis and crystal structure of two potentially useful metal carbonyl complexes: pentacarbonyl(η2-cis-cyclooctene)-tungsten(0) and tetracarbonylbis(η2-cis-cyclooctene)tungsten(0)

W(CO)₅(C₈H₁₄) and W(CO)₄(C₈H₁₄)₂ were synthesized photochemically from W(CO)₆ andcis-cyclooctene with a respective yield of 71% and 18%. The compounds were characterized by NMR, IR and single X-ray crystallography. The IR spectra of the two compounds exhibited characteristic bands for the mono- and bis-substituted metal carbonyl complexes. In W(CO)₄(C₈H₁₄)₂, thecis-cyclooctene ligands are in atrans configuration with the double bonds perpendicular to each other. The two crystal structures were refined toR=0.040 for W(CO)₅(C₈H₁₄) and 0.025 for W(CO)₄(C₈H₁₄)₂. Although the tungsten-carbon (of the carbonyl groups) distances are very similar in both structures, the distances between the tungsten atom and the olefinic carbons are shorter in W(CO)₄(C₈H₁₄)₂, 2.36 Å, than in W(CO)₅(C₈H₁₄), 2.51 Å.     

Assessment of Organic Source Contributions in Coastal Waters by Principal Component and Factor Analysis of the Dissolved and Particulate Hydrocarbon and Fatty Acid Contents

Abstract

Principal component (PCA) and factor analysis (FA) are evaluated for the interpretation of the information contained in large datasets resulting from the study of environmental samples by gas chromatography (GC) and GC coupled to mass spectrometry (GC-MS). A case involving the identification and quantitation of 64 variables (hydrocarbons and fatty acids) in 87 water samples (dissolved and particulate fractions) of a coastal system (Ebre Delta) has been selected for examination.

PCA has evidenced important differences between the dissolved and particulate materials, as well as between the particulates collected in the bays and those obtained in the river and channels. PCA has also allowed the identification of outlier samples in the dissolved fraction. Independent application of FA to each of these groups has provided a useful method for the characterization of diverse algal, terrestrial, microbial and anthropogenic inputs. Direct correspondences between these source inputs and factor loadings have provided a selection of representative components of each contribution in the coastal system.     

Investigation on the reflection at the boundaries for reconstruction laser-based imaging

Optical tomography is acknowledged as an economic and harmless probing technique for medical applications. Recent research tends to show that the use of long term photons, which have travelled a long time in the whole sample to be probed, carry more information in the image reconstruction process. Numerical simulations based on short-pulsed laser beam interaction with non-homogeneous matter are presented. The aim is to emphasize the effect of reflective boundary conditions since reflection enforces photons to stay for a longer period of time in the phantom. It is found that the quality of reconstruction is better when the boundaries are reflecting.